This invention relates to fibers, either in staple or filament form, which exhibit permanent twist without heatsetting and to methods of making such yarn.
Conventional plied yarns are made of either staple or filament yarns. In making a plied yarn from staple yarn, the staple yarn must be processed through carding and drafting, and then spun into a singles yarn. Two or more singles yarns are combined, typically by twisting them together, to form a plied spun yarn. In making a plied yarn from filament yarns two or more singles yarns are combined, typically by twisting them together, to form a plied yarn. The plied yarn (from filament or spun yarn) can be made directly by twisting the two singles yarns, with or without also twisting the individual singles yarn.
In either case, the plied yarns are subsequently treated with heat, called heatsetting, to set the twists permanently into the singles yarns. Heatsetting is considered an essential process in making conventional plied yarns. Without heatsetting, the plied yarns, upon being cut (such as in the manufacture of cut-pile carpet), lose ply-twist at the cut ends. The loss of ply-twist causes the singles yarns (or individual filaments if the yarn is a single ply) to separate from each other, considerably reducing wear performance. Furthermore, compressive forces, like that of foot traffic, will cause the individual filaments to flare and buckle, losing tuft resilience and giving the carpet a worn appearance.
Heatsetting is a labor, energy and capitol intensive process. Thus, heatsetting introduces expense into the manufacturing process. The heatsetting process involves unwinding the yarn to be heatset, heatsetting it and then rewinding it. Not only is it another processing step, but the generation of heat for the heatsetting step is expensive. Moreover, the equipment necessary to heatset requires capital investment. Heatsetting can also cause deleterious changes in the physical properties of yarn, such as shrinkage which may be non-uniform, luster, bulk, dyeability and other properties. It would be advantageous to eliminate the heatsetting step altogether and still obtain the benefits (e.g., locking of twist) achieved by it, without the disadvantages.
In the singles form, a conventional yarn that has been twisted, but not heatset, has torque and will form a tangled mass if tension on it is released, thus making it difficulty to process. It would be advantageous for some end uses to have a torque-free twisted singles yarn.
Accordingly, it is an object of the present invention to provide a singles yarn that will hold twist without heatsetting.
Another object of the present invention is to provide a twisted plied yarn that does not require heatsetting to maintain tuft integrity.
A further object of the present invention is to provide a process for making a twist-set cabled yarn without heatsetting.
A still further object of the present invention is to provide a carpet yarn capable of high twist levels while retaining favorable bulk.
Yet another object of the present invention is to provide a process for making a twist-set cabled yarn that obviates the draw-texturing and heatsetting steps.
Still another object of the present invention is to provide a process for making a twist-set cabled yarn that obviate the texturing and heatsetting steps.
These and related objects and advantages, as be apparent to those of ordinary skill after reading the following detailed description of the invention, are achieved in a self-set yarn comprised of at least one yarn that is comprised of a majority of multicomponent fibers having a first polymer component with a first stress relaxation response and, longitudinally co-extensive therewith, a second polymer component with a second stress relaxation response. The first polymer component and the second polymer component are arranged in a side-by-side or eccentric sheath/core fashion. The yarn is permanently twisted to at least 1 tpi, and the first stress relaxation response and the second stress relaxation response are sufficiently different to produce at least a 10% decrease in length of said yarn.
The yarn preferably has at least two plies of the multifilament yarn which are twisted together. The first polymer component and the second polymer component may both be nylon 6 polymers that differ from each other in relative viscosity.
The present invention is also a process for making self-set yarn. The process comprises the steps of (a)twisting a yarn comprised of a majority of multicomponent fibers having a first polymer component with a first stress relaxation response and, longitudinally co-extensive therewith, a second polymer component of a second stress relaxation response, wherein the first stress relaxation response and the second stress relaxation response are sufficiently different to produce at least a 10% decrease in length of the yarn and wherein the first polymer component and the second polymer component are arranged in a side-by-side or eccentric sheath/core fashion; (b) after said twisting, stressing the resulting twisted yarn; and after said stressing, allowing the twisted yarn to relax. The yarn is twisted to at least 1 tpi and preferably the twisting is ply-twisting together at least two plies of the multifilament yarn The stressing may be a thermal or mechanical stressing.
The products of this invention have self-set characteristics, which offer economic and physical advantages over conventional products by obviating the process of heatsetting and improving yarn bulk, dyeability, appearance retention and many other properties.